Check out the $mech->redirect_ok() option, which instructs your virtual browser (WWW::Mechanize) to follow redirects.

update 1: a simpler approach may be to parse the header yourself looking for a URI to follow. Try the following on one of your magically redirecting pages:

  use WWW::Mechanize;

  my $mech = WWW::Mechanize->new( quiet => 1 );
  $mech->get( "http://www.mysite.com/index.html" );
  die( "Error getting page" ) if ( ! $mech->success() );
  print( $mech->response->headers_as_string );
[download]

or alternatively if you want to see the entire message, headers included, for debugging purposes, replace ->headers_as_string with ->as_string..

Mech already follows valid redirects automatically. These are probably JavaScript or Meta-Refresh tags.

Can you tell us the URL of the page you're trying to access via WWW::Mechanize?

If you're on Windows, you may have better luck with Win32::IE::Mechanize. See this recent thread for some discussion of this module.

Thank you for your answers. Here comes the Link:
http://igs-server.cnrs-mrs.fr/Tcoffee/tcoffee_cgi/index.cgi?action=Make%20a%20multiple%20alignment::Advanced&stage1=1

You will need a dummy file:

>mel
gtaagttttgagcatttaaatggaagtaaaaggcctactagatgggta--------atttgtgttt-acaaagtg---ccagctagggttaccat-gtcgactttgtgttttttccgcatccact-tagcatcagatgatagcattttt-gcaaatttcaagttttacggcgactgtacgagcgcgttccggtccacagcgcactttttccatacgaccgcagtgcgt---ttgtatgcgtttgtgtgtgtatgtacctgatgtctatcttcctcttctgtgtgtttttg---ttgctttttcgttcggggcgaaagtgctactactg--cggtcgttcggaaaaagtgctgctctcaggca--gacgcctcgccgacagtggccttaaaatttgtattcc--acatagcgtggcaaataattactttttcaacg-tgctcataattgcgatttttgatccatag
>sim
gtatgttttgatcacttaaatt-aagtaaaagacctactagatggcta--------atttgtgatt-acaaagtg---ccagctaggcttaccac-gccgactttgtgttttttccgcatccactctagcatcagatgatagcattttttgcaaatttcaagttttacggcgactgtacgagcgcgttccggtccacagcgcactttt-ccatacgaccgcagtgcgc---gtgcatgcgt--gtgtgtgtatgtacctgatatctctcttcctcttctatgtgattctg---ttgctttttcgttcggggcgaaagtgcgaccactg--cggtcgttc-ggaaaagtgctgctctcaaaca--gacgcctcgccgacagtggccgtaaaatttgtattcc--gcatagcgtggcaaataattactttttcaagg-tgctcataattgtgatttttgatccctag
>yak
gtaagttttgtgctcttatgtt-aagtaaaataccttctagccgggcg--------atttgtgatt-acaaagtg---tcagctatgactaccac-gccgactttgtgtttttttcgcatccgct-tagcgtcagatgatagcattttt-gcaaatttcaagttttacggcgactgtacgagcgcgttccggttaacagcgcacttttcccatacgaccgcagtgcgc---ttgtatgcgt--gtgcttgtatgtacctgatgtctctcttcctcttctttgtgttgttg---ctgccttttcgttcggggcgaaagtgcgaccgctg--cggtcgttcgggaaaagtgatgctctccagca--gacgcctcgccgactgtggccgtaaaatgtgtatttc--gcatagcgtggcatataattacaattccaagg-tactcataatcgcgatttttgatccccag
>pse
gtaagtttt-tgca--taaaat-aactaaaaa---ttgtacgcttt-acagcagatatttatgatttac----cggcccccgcagtgtttttcggagccggaggcaaatttttttcgggtccatt-cggcggcggatgatagca-tttt-gcgaatttctagttatacggcgactgtacgagcgcgtttcg--tcagagctcacttttcagtgacaaccgcagagcggattttggtggtgt--gtgtgtat-----------gcttaagtgtg-cgcgtatgtacctgtatgtctgc-ttt--gttc--ggcgaaagtgt-act-ctgaagggttgttgtcgaaaagtgc-gctctgc-gcatggacgcttcagcgaccgtggcggtaaaattt--attttctgcatagcgtggcaattgctcattttttcgccaat-ctaacccttgatatttctgctctccag

That are the options I have chosen:

$mech->form_number(1);
$mech->set_fields(email => "", -uploaded_file => $upload, -case => "upper", -seqnos => "off", -outorder => "input",);
$mech->tick(-in => "Mlalign_id_pair");
$mech->tick(-in => "Mfast_pair");
$mech->tick(-in => "Mclustalw_aln");
$mech->tick(-output => "fasta_aln");
$mech->tick(-output => "score_html");
$mech->submit();